You can also use OPEN INSTALLER to install only the TinyUF2 bootloader, and skip installing CircuitPython.

Choose Install Bootloader Only from the installer menu dialog box.

You will see the dialog boxes for making a serial connection and erasing flash, as described on the Boards With Full USB Support page.

First you'll see Connect to Your Board (click for details) and you'll select the serial port.

Next you'll see the Erase Flash box (click for more details). In general, don't skip erasing the board.

Finally you'll see this Flashing ... box, showing that the installer is flashing TinyUF2 to the board. When it finishes, you'll be done.